A driving circuit for a vibrating-type electromagnetic actuator is known in the art as a driving circuit that drives a resonance system capable of converting or preserving energy through the use of the elasticity of an elastic body and the inertia of a movable body with mass. The vibrating-type electromagnetic actuator includes a stator with a coil, a movable body with a permanent magnet, and a frame portion for reciprocatably supporting the movable body through a spring, the stator being fixed to the frame portion. The driving circuit for this vibrating-type electromagnetic actuator reciprocates the movable body through sensorless feedback control of the application time of an alternating voltage applied to the coil. At this time, a signal indicative of the position where the moving direction of the movable body is inverted (hereinafter referred to as a “phase reference signal”), i.e., a signal indicative of the timing at which the induced electromotive voltage excited in the coil becomes nearly zero, and a signal indicative of the velocity of the movable body ((hereinafter referred to as a “velocity signal”), i.e., the induced electromotive voltage available after a specified time has lapsed from detection of the phase reference signal, are used as control signals (see, e.g., Japanese Patent Laid-open Publication Nos. 7-265560 and 7-313749).
In an effort to reduce the number of parts and to curtail the costs required in installing a sensor, the conventional driving circuit performs the sensorless feedback control in which the induced electromotive voltage is used as one of the control signals. It is, however, impossible to accurately detect the induced electromotive voltage during the time when a magnetizing current or a freewheeling current remains in the coil. Therefore, there is a need to provide a non-magnetizing period within which to detect the induced electromotive voltage. The non-magnetizing period can be provided by predicting the timing at which the phase reference signal appears and then terminating magnetization at the predicted timing without affecting the phase reference signal. When detecting the velocity signal during this non-magnetizing period, a sufficiently amplified voltage and a high enough processing speed of CPU are required in order to detect a minute change in the induced electromotive voltage available after a specified time has lapsed from detection of the phase reference signal. This makes it difficult to construct the driving circuit in a cost-effective manner.